1. Technical Field
The present invention relates to a liquid ejecting head for ejecting a liquid and a liquid ejecting apparatus including the liquid ejecting head. In particular, the invention relates to an inkjet recording head and an inkjet recording apparatus including the inkjet recording head, the inkjet recording head including a vibrating plate constituting part of a pressure-generating chamber communicating with a nozzle opening for ejecting ink droplets; and a piezoelectric element disposed on the vibrating plate, and the inkjet recording head ejecting ink droplets by displacement of the piezoelectric element.
2. Related Art
In inkjet recording heads that each include a vibrating plate constituting part of a pressure-generating chamber communicating with a nozzle opening for ejecting ink and that each eject ink from the nozzle opening by deforming the vibrating plate using a piezoelectric element and pressurizing the ink in the pressure-generating chamber, the following two types of heads have been in practical use: a head including a longitudinal-vibration-mode piezoelectric actuator extending and shrinking in the axial direction of the piezoelectric element; and a head including a flexural-vibration-mode piezoelectric actuator.
An example of the head including the actuator operating in the flexural vibration mode is a head including a piezoelectric element produced by forming a uniform piezoelectric material layer over a vibrating plate using a film-forming technique and then separating the resulting piezoelectric material layer into pieces each having a shape corresponding to a pressure-generating chamber using lithography to form separate piezoelectric elements corresponding to the individual pressure-generating chambers. Such a piezoelectric element has a disadvantage that, for example, the element is easily fractured by external environment such as moisture.
For example, Japanese Patent No. 3,552,013 (Patent Document 1, see, page 4, FIG. 4) discloses a head structure for preventing a piezoelectric element from fracturing and for not inhibiting deformation of the piezoelectric element, the head structure including a thin insulating film composed of, for example, a silicon oxide, a silicon nitride, or an organic material and preferably a photosensitive polyimide, and the head covering at least the periphery of the top face of an upper electrode constituting the piezoelectric element and covering side faces of a piezoelectric layer.
For example, JP-A-2001-260357 (Patent Document 2, see pages 5 and 6, FIGS. 7 and 8) a head structure for preventing a piezoelectric element from fracturing and for not inhibiting deformation of the piezoelectric element, the head structure including a protective insulating film that is disposed over the piezoelectric element and that has a thin portion at a region corresponding to a main portion of an upper electrode, the thin portion having a thickness smaller than the other region.
However, in the structure described in Patent Document 1, ends of an upper electrode-exposing region in the longitudinal direction are not defined. In the case where the ends are disposed outside ends of a piezoelectric active portion, which is a substantial driving portion, when the piezoelectric element is deformed in the flexural mode, stress disadvantageously concentrates in the vicinities of the ends of the electrode-exposing region, thereby fracturing the piezoelectric element.
In Patent Document 2, providing the thin portion of the protective film disposed on the surface of the upper electrode can result in the prevention of the fracture due to external environment of the piezoelectric element. However, the thin portion is formed by adjusting etching time, i.e., by half-etching; hence, it is difficult to control the thickness of the thin portion and to produce a piezoelectric element having uniform displacement properties. Furthermore, the thickness of the thin portion can be controlled by further forming the thin portion after the exposure of the surface of the upper electrode. However, the number of production steps of forming the thin portion disadvantageously increases, thus disadvantageously increasing cost and complexity. Moreover, the thin portion disadvantageously reduces the amount of flexural deformation of the piezoelectric element to degrade ink-ejecting properties.
Note that the above-described problems exist in liquid ejecting heads for ejecting liquid other than ink as well as in the inkjet recording heads for ejecting ink.